<p>We conduct a systematic investigation of freeze-in during reheating while taking care to include both direct and indirect production of dark matter (DM) via gravitational portals and inflaton decay. Direct production of DM can occur via gravitational scattering of the inflaton, while indirect production occurs through scattering in the Standard Model radiation bath. We consider two main contributions to the radiation bath during reheating. The first, which may dominate at the onset of the reheating process, is produced via gravitational scattering of the inflaton. The second (and more standard contribution) comes from inflaton decay. We consider a broad class of DM production rates parametrized as <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>R</mi><mi>χ</mi></msub><mo>∝</mo><msup><mi>T</mi><mrow><mi>n</mi><mo>+</mo><mn>6</mn></mrow></msup><mo>/</mo><msup><mi mathvariant="normal">Λ</mi><mrow><mi>n</mi><mo>+</mo><mn>2</mn></mrow></msup></math>, and inflaton potentials with a power-law form <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>V</mi><mo stretchy="false">(</mo><mi>ϕ</mi><mo stretchy="false">)</mo><mo>∝</mo><msup><mi>ϕ</mi><mi>k</mi></msup></math> about the minimum. We find the relic density produced by freeze-in for each contribution to the Standard Model bath for arbitrary <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>k</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>n</mi></math>, and compare these with the DM density produced gravitationally by inflaton scattering. We find that freeze-in production from the gravitationally produced radiation bath can exceed that of the conventional decay bath and account for the observed relic density provided that <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>m</mi><mi>χ</mi></msub><mo>&gt;</mo><msub><mi>T</mi><mrow><mi>RH</mi></mrow></msub></math>, with additional <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>k</mi></math>- and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>n</mi></math>-dependent constraints. For each freeze-in interaction considered, we also find <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>m</mi><mi>χ</mi></msub></math>- and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>T</mi><mrow><mi>RH</mi></mrow></msub></math>-dependent limits on the beyond the Standard Model scale, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="normal">Λ</mi></math>, for which gravitational production will exceed ordinary freeze-in production.</p>

United States

Stephen E. Henrich

France

Yann Mambrini

Keith A. Olive

Aspects of gravitational portals and freeze-in during reheating

<p>We calculate the gravitational waves (GWs) produced by primordial black holes (PBHs) in the presence of the inflaton condensate in the early Universe. Combining the GW production from the evaporation process, the gravitational scattering of the inflaton itself, and the density fluctuations due to the inhomogeneous distribution of PBHs, we propose for the first time a complete coherent analysis of the spectrum, revealing three peaks, one for each source. Three frequency ranges (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo>∼</mo><mi>kHz</mi></math>, GHz, and PHz, respectively) are expected, each giving rise to a similar GW peak amplitude <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi mathvariant="normal">Ω</mi><mi>GW</mi></msub></math>. We also compare our predictions with current and future GWs detection experiments.</p>

Mathieu Gross

Spain

Essodjolo Kpatcha

United Kingdom

Maria Olalla Olea-Romacho

Rishav Roshan

Gravitational wave production during reheating: From the inflaton to primordial black holes

We give a fresh look at the WIMP paradigm by considering updated limits and prospects for direct and indirect dark matter detection and covering realistic dark matter models, beyond the so-called simplified models, which have been the target of experimental scrutiny. In particular, we investigate dark matter scenarios featuring dwindled direct detection signals, due to loop or momentum suppression. Therefore, this review extends previous reviews in different aspects and motivates the search for WIMP dark matter in light of the present and near-future detectors.

Italy

Giorgio Arcadi

David Cabo-Almeida

Maíra Dutra

India

Pradipta Ghosh

Germany

Manfred Lindner

Brazil

Jacinto Neto

Mathias Pierre

Stefano Profumo

Chile

Farinaldo Queiroz

The waning of the WIMP: endgame?

We study the effects on particle production of a Planck-suppressed coupling between the inflaton and a scalar dark matter candidate, <math><mi>χ</mi></math>. In the absence of this coupling the dominant source for the relic density of <math><mi>χ</mi></math> is the long wavelength modes produced from the scalar field fluctuations during inflation. In this case, there are strong constraints on the mass of the scalar and the reheating temperature after inflation from the present-day relic density of <math><mi>χ</mi></math> (assuming <math><mi>χ</mi></math> is stable). When a coupling <math><mi>σ</mi><msup><mi>ϕ</mi><mn>2</mn></msup><msup><mi>χ</mi><mn>2</mn></msup></math> is introduced, with <math><mi>σ</mi><mo>=</mo><mover><mi>σ</mi><mo>˜</mo></mover><msubsup><mi>m</mi><mi>ϕ</mi><mn>2</mn></msubsup><mo>/</mo><msubsup><mi>M</mi><mi>P</mi><mn>2</mn></msubsup><mo>∼</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>10</mn></mrow></msup><mover><mi>σ</mi><mo>˜</mo></mover></math>, where <math><msub><mi>m</mi><mi>ϕ</mi></msub></math> is the inflaton mass, the allowed parameter space begins to open up considerably even for <math><mover><mi>σ</mi><mo>˜</mo></mover></math> as small as <math><mo>≳</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>7</mn></mrow></msup></math>. For <math><mover><mi>σ</mi><mo>˜</mo></mover><mo>≳</mo><mfrac><mn>9</mn><mn>16</mn></mfrac></math>, particle production is dominated by the scattering of the inflaton condensate, either through single graviton exchange or the contact interaction between <math><mi>ϕ</mi></math> and <math><mi>χ</mi></math>. In this regime, the range of allowed masses and reheating temperatures is maximal. For <math><mn>0.004</mn><mo>&lt;</mo><mover><mi>σ</mi><mo>˜</mo></mover><mo>&lt;</mo><mn>50</mn></math>, constraints from isocurvature fluctuations are satisfied, and the production from parametric resonance can be neglected.

Gongjun Choi

Mexico

Marcos A. G. Garcia

Wenqi Ke

Sarunas Verner

Inflaton production of scalar dark matter through fluctuations and scattering

We explore the possibility of producing the observed matter-antimatter asymmetry of the Universe uniquely from the evaporation of primordial black holes (PBHs) that are formed in an inflaton-dominated background. Considering the inflaton <math><mo>(</mo><mi>ϕ</mi><mo>)</mo></math> to oscillate in a monomial potential <math><mi>V</mi><mo>(</mo><mi>ϕ</mi><mo>)</mo><mo>∝</mo><msup><mi>ϕ</mi><mi>n</mi></msup></math>, we show, it is possible to obtain the desired baryon asymmetry via vanilla leptogenesis from evaporating PBHs of initial mass <math><mo>≲</mo><mn>10</mn><mtext> </mtext><mtext> </mtext><mi>g</mi></math>. We find that the allowed parameter space is heavily dependent on the shape of the inflaton potential during reheating (determined by the exponent of the potential <math><mi>n</mi></math>), the energy density of PBHs (determined by <math><mi>β</mi></math>), and the nature of the coupling between the inflaton and the Standard Model. To complete the minimal gravitational framework, we also include in our analysis the gravitational leptogenesis setup through inflaton scattering via exchange of graviton, which opens up an even larger window for PBH mass, depending on the background equation of state. We finally illustrate that such gravitational leptogenesis scenarios can be tested with upcoming gravitational wave (GW) detectors, courtesy of the blue-tilted primordial GW with inflationary origin, thus paving a way to probe a PBH-induced reheating together with leptogenesis.

Basabendu Barman

South Korea

Suruj Jyoti Das

Md Riajul Haque

Leptogenesis, primordial gravitational waves, and PBH-induced reheating

We consider the effects of a bare mass term for the inflaton, when the inflationary potential takes the form <math><mrow><mi>V</mi><mo>(</mo><mi>ϕ</mi><mo>)</mo><mo>=</mo><mi>λ</mi><msup><mrow><mi>ϕ</mi></mrow><mrow><mi>k</mi></mrow></msup></mrow></math> about its minimum with <math><mi>k</mi><mo>≥</mo><mn>4</mn></math>. We concentrate on <math><mi>k</mi><mo>=</mo><mn>4</mn></math>, but discuss general cases as well. Further, we assume <math><mrow><mi>λ</mi><msubsup><mrow><mi>ϕ</mi></mrow><mrow><mi>end</mi></mrow><mrow><mn>2</mn></mrow></msubsup><mo>≫</mo><msubsup><mrow><mi>m</mi></mrow><mrow><mi>ϕ</mi></mrow><mrow><mn>2</mn></mrow></msubsup></mrow></math>, where <math><msub><mi>ϕ</mi><mrow><mi>end</mi></mrow></msub></math> is the inflaton field value when the inflationary expansion ends. We show that the presence of a mass term (which may be present due to radiative corrections or supersymmetry breaking) can significantly alter the reheating process, as the equation of state of the inflaton condensate changes from <math><msub><mi>w</mi><mi>ϕ</mi></msub><mo>=</mo><mfrac><mn>1</mn><mn>3</mn></mfrac></math> to <math><msub><mi>w</mi><mi>ϕ</mi></msub><mo>=</mo><mn>0</mn></math> when <math><mi>λ</mi><msup><mi>ϕ</mi><mn>2</mn></msup></math> drops below <math><msubsup><mi>m</mi><mi>ϕ</mi><mn>2</mn></msubsup></math>. We show that, for a mass <math><mrow><msub><mrow><mi>m</mi></mrow><mrow><mi>ϕ</mi></mrow></msub><mo>≳</mo><mn>3</mn><msup><mrow><mi>λ</mi></mrow><mrow><mfrac><mrow><mn>1</mn></mrow><mrow><mn>4</mn></mrow></mfrac></mrow></msup><msub><mrow><mi>T</mi></mrow><mrow><mi>RH</mi></mrow></msub></mrow></math>, the mass term will dominate at reheating. The value of <math><mi>λ</mi></math> is relatively model independent as it is normalized by the cosmic microwave background perturbation spectrum. For T models of inflation, this leads to <math><mrow><msub><mrow><mi>m</mi></mrow><mrow><mi>ϕ</mi></mrow></msub><mo>≳</mo><msub><mrow><mi>T</mi></mrow><mrow><mi>RH</mi></mrow></msub><mo>/</mo><mn>250</mn></mrow></math>. We compute the effects on the reheating temperature for cases where reheating is due to inflaton decay (to fermions, scalars, or vectors) or to inflaton scattering (to scalars or vectors). For scattering to scalars and in the absence of a decay, there is always a residual inflaton background that acts as cold dark matter. In this case, we derive a strong upper limit to the inflaton bare mass which for T models is <math><mrow><msub><mrow><mi>m</mi></mrow><mrow><mi>ϕ</mi></mrow></msub><mo>&lt;</mo><mn>350</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi><mo>(</mo><msub><mrow><mi>T</mi></mrow><mrow><mi>RH</mi></mrow></msub><mo>/</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>10</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>GeV</mi><msup><mrow><mo>)</mo></mrow><mrow><mn>3</mn><mo>/</mo><mn>5</mn></mrow></msup></mrow></math>. We also consider the effect of the bare mass term on the fragmentation of the inflaton condensate.

Simon Clery

Bare mass effects on the reheating process after inflation

We compare the dark matter (DM) production processes and its parameters space in the background of reheating obtained from two chief systems in the early Universe: the inflaton <math><mi>ϕ</mi></math> and the primordial black holes (PBHs). We concentrated on the mechanism where DMs are universally produced only from the PBH decay and the generation of the standard model plasma from both inflaton and PBHs. Whereas the distribution of primordial black holes behaves like dust, the inflaton phenomenology depends strongly on its equation of state after the inflationary phase, which in turn is conditioned by the nature of the potential <math><mi>V</mi><mo>(</mo><mi>ϕ</mi><mo>)</mo></math>. Depending upon the initial mass and population of PBHs, a large range of DM mass is shown to be viable if reheating is controlled by PBHs itself. Inflaton-dominated reheating is observed to further widen such possibilities depending on the initial population of black holes and its mass as well as the coupling of the inflaton to the standard model sector.

Debaprasad Maity

Primordial black hole versus inflaton

We compute the density of a spin-<math><mfrac><mn>3</mn><mn>2</mn></mfrac></math> particle, the raritron, produced at the end of inflation due to gravitational interactions. We consider a background inflaton condensate as the source of this production, mediated by the exchange of a graviton. This production greatly exceeds the gravitational production from the emergent thermal bath during reheating. The relic abundance limit sets an absolute minimum mass for a stable raritron, though there are also model-dependent constraints imposed by unitarity. We also examine the case of gravitational production of a gravitino, taking into account the goldstino evolution during reheating. We compare these results with conventional gravitino production mechanisms.

Japan

Kunio Kaneta

Gravitational production of spin-<math><mrow><mn>3</mn><mo>/</mo><mn>2</mn></mrow></math> particles during reheating

The postinflationary reheating phase is usually said to be solely governed by the decay of coherently oscillating inflatons into radiation. In this submission, we explore a new avenue towards reheating through the evaporation of primordial black holes (PBHs). After the inflation, if PBHs form, depending on its initial mass, abundance, and inflaton coupling with the radiation, we found two physically distinct possibilities of reheating the Universe. In one possibility, the thermal bath is solely obtained from the decay of PBHs while inflaton plays the role of the dominant energy component in the entire process. In the other possibility, we found that PBHs dominate the total energy budget of the Universe during the course of evolution, and then its subsequent evaporation leads to a radiation dominated universe. Furthermore, we analyze the impact of both monochromatic and extended PBH mass functions and estimate the detailed parameter ranges for which those distinct reheating histories are realized.

Primordial black hole reheating

We study the effects of an anomalous Z′ boson on the anomalous magnetic moment of the muon (g – 2), and especially the impact of its axial coupling. We mainly evaluate the negative contribution to (g – 2) of such couplings at one-loop and look at the anomalous couplings generated at two loops. We find areas of the parameter space, where the anomalous contribution becomes comparable and even dominant compared to the one-loop contribution. We show that in such cases, the cutoff of the theory is sufficiently low, so that new charged fermions can be found in the next round of collider experiments. We comment on the realization of such a context in string theory orientifolds.